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Type: Thesis
Title: The effects of high temperature metamorphic and melting processes on granulite-facies rocks
Author: Alessio, Kiara Louise
Issue Date: 2019
School/Discipline: School of Physical Sciences : Earth Sciences
Abstract: This thesis presents research on high-temperature metamorphic processes. A recent development in petrological modelling of granulite facies rocks is reintegration of melt generated and lost during metamorphism. The aim of melt reintegration is to create bulk compositions suitable for modelling prograde subsolidus evolution. Melt reintegration methodology was applied to a low-pressure granulite assemblage containing unambiguous textural evidence for subsolidus andalusite. Melt reintegration methodology resulted in a bulk composition that stabilised subsolidus and modally correct andalusite, providing validation of this petrological modelling technique. Melting and melt loss modifies rock chemistry and a long-standing paradigm is that melting depletes rocks in heat producing elements (HPEs). However, comprehensive K–U–Th datasets taken from a number of terranes show that in metapelites, melting and melt loss does not deplete U–Th concentrations, with overall terrane averages suggesting bulk heat production partitioning between melt and residuum is essentially 1:1. Modelling of HPE concentrations derived from terrane-scale elemental mapping in central Australia show that low-pressure (150–175 °C/kbar) granulite-facies metamorphism was driven by elevated crustal heat production. This energy source resulted in extremely long-lived (> 150 Ma) low-P–high-T metamorphism. High thermal gradient metamorphism driven by this energy source is characterised by contractional structures, kinematically late temperature maxima, and tight clockwise P–T loops. Petrochronology (the nexus between the isotopic age of a mineral and its compositional controls) is being increasingly used to interrogate the thermobarometric record contained in metamorphic rocks. Combined zircon and monazite REE-isotopic U–Pb compositions from interlayered metapelite and metabasic granulites show essentially identical peak metamorphic assemblages were achieved by substantially different P–T–t paths. The metabasic rock composition reached peak conditions at least 30 Ma before the metapelite. While speculative, the thermal delay recorded by the metapelite may reflect thermal buffering associated with partial melting and persistent structurally focussed melt streaming.
Advisor: Hand, Martin
Kelsey, David
Morrissey, Laura
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2019
Keywords: Metamorphic geology
radiogenic heat production
phase equilibria modelling
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