Long‐lived high‐T, low‐P granulite facies metamorphism in the Arunta Region, central Australia

Abstract

In situ LA-ICP-MS U-Pb monazite geochronology from the Boothby Hills in the Aileron Province, central Australia, indicates that the region records more than 80 Ma of hightemperature, low-pressure (HTLP) anatectic conditions during the Early Mesoproterozoic. Monazite ages from granulite facies rocks and leucosomes span the interval 1576-1542 Ma. Pegmatites that overprint the regional gneissic fabric and are interpreted to record the last vestiges of melt crystallization give ages between 1523-1513 Ma. Calculated P-T pseudosections suggest peak metamorphic conditions in excess of 850 °C at 0.65-0.75 GPa, with the retrograde evolution characterised by a P-T path that involved minor decompression and then cooling, culminating with the development of andalusite. Integration of the geochronological dataset with the inferred P-T path trajectory suggests that suprasolidus cooling must have been slow, in the order of 2.5 to 4 °C Ma -1 . In addition, the retrograde P-T path trajectory suggests that HTLP conditions were generated within crust of relatively normal thickness. Despite the long duration over which anatectic conditions occurred, there is no evidence for external magmatic inputs or evidence that HTLP conditions were associated with long-lived extension. Instead, it seems probable that the long-lived HTLP metamorphism was driven to a significant extent by longlived conductive heating provided by high crustal heat production in voluminous premetamorphic granitic rocks.

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

“…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.…”

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

“…However, in either case, the diffuse nature strongly suggests the rock containing the leucosomes was suprasolidus at the time the leucosomes were generated, and the field relationships suggest melt was present during the suprasolidus retrograde PeT evolution (e.g. Anderson et al, 2013;Morrissey et al, 2014;Yakymchuk and Brown, 2014b). Additionally, the existence of melt in granulite and UHT rocks during at least part of the retrograde history is provided by its requirement for balancing retrograde reactions that have not gone to completion (e.g.…”

“…The amount of melt chosen to be integrated should be guided by the critical threshold deemed to apply for melt loss in rocks (i.e. approximately 7 mol% melt; Rosenberg and Handy, 2005;Brown and Korhonen, 2009;Brown, 2010a;Yakymchuk et al, 2013;Yakymchuk and Brown, 2014b) as well as by how abundant evidence for 'late' melt is in the terrane (Greenfield et al, 1996;Anderson et al, 2013;Morfin et al, 2013;Morrissey et al, 2014). The TeM melt section method provides an estimation of H 2 O in the context of the full NCKFMASH composition of silicate melt and also allows for quantitative appraisal of the effect of the abundance of melt on the temperature location of the solidus (Anderson et al, 2013;Morrissey et al, 2013).…”

Continuous zircon growth during long-lived granulite facies metamorphism: a microtextural, U–Pb, Lu–Hf and trace element study of Caledonian rocks from the Arctic

“…However, due to the prolonged higher temperatures experienced by the rocks of the Chukchi Borderland, it is reasonable to assume that the rocks experienced limited exhumation during metamorphism. Similar high-T, long-lived metamorphic events have been described in the Eastern Ghats orogenic belt (India), Arunta region (central Australia) and southwestern Madagascar (Ashwal et al 1999;Korhonen et al 2013;Morrissey et al 2014). …”