Conductively driven, high-thermal gradient metamorphism in the Anmatjira Range, Arunta region, central Australia

Abstract

<jats:title>Abstract</jats:title><jats:p>LA<jats:italic>–</jats:italic>ICP<jats:italic>–</jats:italic>MS <jats:italic>in situ</jats:italic> U–Pb monazite geochronology and <jats:italic>P–T</jats:italic> pseudosections are combined to evaluate the timing and physical conditions of metamorphism in the SE Anmatjira Range in the Aileron Province, central Australia. All samples show age peaks at <jats:italic>c</jats:italic>. 1580<jats:italic>–</jats:italic>1555 Ma, with three of five samples showing additional discrete age peaks between <jats:italic>c</jats:italic>. 1700 and 1630 Ma. <jats:italic>P–T</jats:italic> phase diagrams calculated for garnet<jats:italic>–</jats:italic>sillimanite<jats:italic>–</jats:italic>cordierite<jats:italic>–</jats:italic>K‐feldspar<jats:italic>–</jats:italic>ilmenite–melt bearing metapelitic rocks have overlapping peak mineral assemblage stability fields at ~870<jats:italic>–</jats:italic>920 °C and ~6.5<jats:italic>–</jats:italic>7.2 kbar. <jats:italic>P–T</jats:italic> modelling of a fine‐grained spinel<jats:italic>–</jats:italic>cordierite<jats:italic>–</jats:italic>garnet<jats:italic>–</jats:italic>biotite reaction microstructure suggests retrograde <jats:italic>P–T</jats:italic> conditions evolved down pressure and temperature to ~3–5.5 kbar and ~610–850 °C. The combined geochronological and <jats:italic>P–T</jats:italic> results indicate the SE Anmatjira Range underwent high‐temperature, low‐pressure metamorphism at <jats:italic>c</jats:italic>. 1580<jats:italic>–</jats:italic>1555 Ma, and followed an apparently clockwise retrograde path. The high apparent thermal gradient necessary to produce the estimated <jats:italic>P–T</jats:italic> conditions does not appear to reflect decompression of high‐<jats:italic>P</jats:italic> assemblages, nor is there syn‐metamorphic magmatism or structural evidence for extension. Similar to previous workers, we suggest the high‐thermal gradient <jats:italic>P–T</jats:italic> conditions could have been achieved by heating, largely driven by high heat production from older granites in the region.</jats:p>