Unravelling the tectonothermal evolution of reworked Archean granulite facies metapelites using in situ geochronology: an example from the Gawler Craton,Australia |
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| Authors: | R A DUTCH M HAND D E KELSEY |
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| Institution: | 1. Present address: Geological Survey Branch, Department of Primary Industries and Resources South Australia, Adelaide 5001, Australia.;2. Centre for Tectonics, Resources and Exploration, University of Adelaide, Adelaide 5005, Australia (riandutch@gmail.com) |
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| Abstract: | The use of in situ geochronological techniques allows for direct age constraints to be placed on fabric development and the metamorphic evolution of polydeformed and reworked terranes. The Shoal Point region of the southern Gawler Craton consists of a series of reworked granulite facies metapelitic and metaigneous units which belong to the Late Archean Sleaford Complex. Structural evidence indicates three phases of fabric development with D1 retained within boudins, D2 consisting of a series of upright open to isoclinal folds producing an axial planar fabric and D3 composed of a highly planar vertical high‐strain fabric which overprints the D2 fabric. Th–U–total Pb EPMA monazite and garnet Sm–Nd geochronology constrain the D1 event to the c. 2450 Ma Sleaford Orogeny, whereas the D2 and D3 events are constrained to the 1730–1690 Ma Kimban Orogeny. P–T pseudosections constrain the metamorphic conditions for the Sleafordian Orogeny to between 4.5 and 6 kbar and between 750 and 780 °C. Subsequent Kimban‐aged reworking reached peak metamorphic conditions of 8–9 kbar at 820–850 °C during the D2 event, followed by high‐temperature decompression to metamorphic conditions <6 kbar and 790–850 °C associated with the development of the D3 high‐strain fabric. The P–T–t evolution of the Shoal Point rocks reflects the transpressional exhumation of lower crustal rocks during the Kimban Orogeny and the development of a regional ‘flower structure’. |
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| Keywords: | Gawler Craton in situ geochronology metapelites P– T– t evolution reworking |
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