Unravelling the tectonothermal evolution of reworked Archean granulite facies metapelites using in situ geochronology: an example from the Gawler Craton, Australia

Abstract

<jats:title>Abstract</jats:title><jats:p>The use of <jats:italic>in situ</jats:italic> 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 <jats:italic>D</jats:italic><jats:sub>1</jats:sub> retained within boudins, <jats:italic>D</jats:italic><jats:sub>2</jats:sub> consisting of a series of upright open to isoclinal folds producing an axial planar fabric and <jats:italic>D</jats:italic><jats:sub>3</jats:sub> composed of a highly planar vertical high‐strain fabric which overprints the <jats:italic>D</jats:italic><jats:sub>2</jats:sub> fabric. Th–U–total Pb EPMA monazite and garnet Sm–Nd geochronology constrain the <jats:italic>D</jats:italic><jats:sub>1</jats:sub> event to the <jats:italic>c.</jats:italic> 2450 Ma Sleaford Orogeny, whereas the <jats:italic>D</jats:italic><jats:sub>2</jats:sub> and <jats:italic>D</jats:italic><jats:sub>3</jats:sub> events are constrained to the 1730–1690 Ma Kimban Orogeny. <jats:italic>P–T</jats:italic> 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 <jats:italic>D</jats:italic><jats:sub>2</jats:sub> event, followed by high‐temperature decompression to metamorphic conditions &lt;6 kbar and 790–850 °C associated with the development of the <jats:italic>D</jats:italic><jats:sub>3</jats:sub> high‐strain fabric. The <jats:italic>P–T–t</jats:italic> 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’.</jats:p>