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

Abstract

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

Genesis of the central zone of the Nolans Bore rare earth element deposit, Northern Territory, Australia

“…400 Ma. The calculated isotopic composition of the alteration zone fluids (4.8-6.0 ‰; Table 2) is below the values of crustal rocks of the Reynolds Range , but is consistent with a mixed meteoric fluid/metamorphic fluid source, as has been proposed to explain similar isotopic signatures for Alice Springs shear zone fluids (Anderson et al 2013(Anderson et al , 1999Cartwright et al 2000;Read and Cartwright 2000;Raimondo et al 2011). …”

“…of metamorphism is suggested to be caused by deepseated high-heat-producing granites (Rubatto et al 2001;Anderson et al 2013;Morrissey et al 2014), although there is no known magmatism of significance correlated with this event (Scrimgeour 2006). Nevertheless, Anderson et al (2013) and Morrissey et al (2014) suggest that the late pegmatites at Mt Boothby, dated at 1523 ± 8 Ma and 1513 ± 15 Ma, also belong to the Chewings Orogeny as there is no other evidence of a thermal event at this age. These ages also correlate with the expected age of the primary mineralisation at Nolans Bore (ca.…”

“…1600-1520 Ma-the Chewings Orogeny: in the Reynolds Range, this event caused a metamorphic overprint, ranging from greenschist facies (ca. 400 °C) in the north-west to granulite facies (0.4-0.7 GPa, 700 to >850 °C) with associated anatexis and deformation in the south-east (Dirks et al 1991;Claoué-Long et al 2008;Anderson et al 2013;Morrissey et al 2014). The high temperature and duration (ca.…”

“…This intraplate orogenic event is deemed to be responsible for most of the current topography and the current juxtaposition of granulite and greenschist facies Proterozoic rocks in the region (Claoué-Long and Hoatson 2005). Tectonic activity involved north-south shortening, most of which was accommodated by deformation and uplift of the region via the reactivation of the Redbank Shear Zone (Hand and Sandiford 1999;Roberts and Houseman 2001) and initiation of other large (>100 m wide) hydrous shear zones (Collins and Teyssier 1989;Raimondo et al 2011;Anderson et al 2013). Thermobarometry studies estimate the conditions of metamorphism in the Reynolds Ranges during the Alice Springs Orogeny reached ca.…”

LA-ICP-MS U–Pb dating of detrital rutile and zircon from the Reynolds Range: A window into the Palaeoproterozoic tectonosedimentary evolution of the North Australian Craton

“…Age constraints for the Coniston Schist are based on Smith (2001) and for the Anmatjira Orthogneiss on Rubatto et al (2006) and Worden et al (2008a). Maidment et al, 2005;Scrimgeour et al, 2005;Claoué-Long and Edgoose, 2008;Raimondo et al, 2011;Anderson et al, 2013).…”