Th–U powered metamorphism: Thermal consequences of a chemical hotspot

Abstract

The Arkaroola region of the northern Flinders Ranges, South Australia, records high geothermal gradient mineral assemblages that are not spatially or temporally associated with intrusive magmatism. Cordierite-bearing schists from the base of a ~12 km thick Neoproterozoic sedimentary sequence known as the Adelaide Rift Complex directly overlie Mesoproterozoic metasedimentary and granitic rocks with regional heat production values of ~7.9 µW/m 3 at 580 Ma, two to three times greater than global average values for granitic rocks. We integrate in-situ U-Pb monazite geochronology, Y+HREE-in-monazite thermometry and mineral equilibria modelling to show that rocks at the base of the sedimentary succession record amphibolite facies metamorphism at c. 580 Ma while the overlying sediments were still accumulating. Metamorphism took place under average geothermal gradient conditions in excess of 180°C/kbar (>60°C/km) that propagated to depths of at least 12 km. These thermal gradients persisted for upwards of 150 Ma, maintained by a lack of crustal erosion, and are documented by long-lived crustal anatexis. This system may be the archetypal example of Th-U powered metamorphism, recording the interplay between chemically extreme basement and thermally insulating sedimentary cover.

HTLP metamorphism and fluid‐fluxed melting during multistage anatexis of continental crust (N Sardinia, Italy)

“…Depine et al, 2008). Alternatively, several authors argue that HTLP metamorphism is most effectively caused by protracted crustal reworking leading to selective enrichment in U, Th, K and other heat‐producing elements (Sandiford & McLaren, 2002; Gerdes et al, 2000; Rudnick & Gao, 2003; Jaupart & Marechal, 2007; Kumar et al, 2007; Lexa et al, 2011; De Vraies van Leeuwen et al, 2021). The last model has been demonstrated as an effective thermal source yielding to the development of orogen‐scale thermal anomalies that can persist over millions of years (Burg & Gerya, 2005; Nabelek et al, 2001).…”

Intracontinental Fault Reactivation in High Heat Production Areas of Central Australia: Insights From Apatite Fission Track Thermochronology

“… (a) Surface radiogenic heat production map of central Australia calculated at 250 Ma during the latter stages of Tasmanide deformation, following methodology of De Vries Van Leeuwen et al. (2021). Modern U, Th, and K abundances as determined by radiometric surveys (Minty et al., 2009, 2010) were extrapolated back in time based on respective isotopic decay constants to determine concentrations at 250 Ma, and transformed to radiogenic heat production using the expected heat production attributed to each element.…”

Coupled Microstructural EBSD and LA-ICP-MS Trace Element Mapping of Pyrite Constrains the Deformation History of Breccia-Hosted IOCG Ore Systems

“…A first consideration is South Australia's enrichment in heat producing elements (HPE) which is shown to generate anomalously elevated geothermal gradients and heat flows across the region [83]. This has produced the South Australian Heat Flow Anomaly in which heat flow is two to three times above average and can drive high temperature-low pressure metamorphism (e.g., [83][84][85]). In the Yorke Peninsula, SE Gawler Craton, Bockmann et al [85] found evidence for a metamorphic event between 1.56-1.5 Ga, thermally driven by this HPE heat anomaly at P-T conditions of 660-750 • C and 3.6-5.5 kbar.…”