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Title: Refining the physical and temporal record of metamorphism during the Delamerian Orogeny
Author: Stinear, M. D.
Issue Date: 2017
School/Discipline: School of Physical Sciences
Abstract: The Delamerian Orogen formed via convergence against the southeastern margin of the Gawler Craton during the Late Cambrian and is characterised by low-P, high-T metamorphism. The evolution of the Delamerian Orogen has been extensively studied by several authors through U-Pb zircon and Sm/Nd geochronology, but lacks fundamental characterisation of its thermal history. Metamorphic studies, of where there are few, suggest an ‘anticlockwise’ P-T evolution for the Delamerian Orogen. Garnet-staurolite-andalusite-bearing and sillimanite-bearing metapelites in this study were investigated using U-Pb LA-ICP-MS and have metamorphic monazite ages between 514-480Ma. Calculated phase equilibria modelling constrains metamorphism in the andalusite-staurolite-bearing schists to ~4.6kbar and 570°C, to 3.7kbar and 635°C in the sillimanite-bearing schists, and 1.0-4.4kbar and 790-860°C in the highest-grade parts of the orogen. The coupled 206Pb/238U monazite ages and phase equilibria modelling suggest that the crust deformed in temporal association with the repeated intrusions of granitic material that weakened the comparatively rigid mid-upper crust, leading to the formation of temporally discrete ‘anticlockwise’ P-T paths. Older metamorphic ages on Kangaroo Island and younger ages on mainland South Australia indicate that the thermal locus moved northwards over time, resulting in a metamorphic terrain that gives the appearance of a patchwork orogen of discrete metamorphic subdomains, with the highest-grades surrounding granitic intrusions which occur late in the evolution of the Delamerian Orogen.
Dissertation Note: Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2017
Where: Kanmantoo Trough, Delamerian Orogen, Fleurieu Peninsula, South Australia
Keywords: Honours; Geology; Delamerian Orogeny; metamorphism; monazite; U-Pb geochronology; P-T pseudosection
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