A time frame for protracted multiphase metamorphism, magmatism and deformation in the exhumed core of the Alice Springs Orogen, Harts Range, central Australia

Abstract

The Harts Range Metamorphic Complex (HRMC) in the eastern Arunta Province is part of the exhumed core of the intracratonic Alice Springs Orogen. SHRIMP U-Pb dating of intrusive rocks and metamorphism in the HRMC has constrained the timing and character of tectonism, showing that mutliphase deformation under high grade metamorphic conditions spanned at least 50 m.y. The age of a syn-tectonic pegmatite dyke in the northern HRMC records ductile shearing on E-W trending shear zones during or just after the ~380 Ma Pertnjara Movement, possibly related to extension after the main contractional phase. The age of a second syn- to late-deformational pegmatite dyke in the eastern Harts Range suggests that a SW-vergent fold and thrust system in the eastern HRMC formed during the ~360 Ma Brewer Movement. This deformation coincided with the intrusion of small granitic bodies in the northern HRMC, and the formation of rare metamorphic zircon in metasedimentary rocks during a period of crustal thickening. Metamorphic monazite and zircon reflect high-grade metamorphism during the ~330 Ma Mount Eclipse Movement, which coincided with the formation of a flat-lying, kyanite grade foliation in basement rocks of the HRMC. This foliation and later large-scale doming might reflect extensional collapse of the Alice Springs Orogen towards the end of the orogenic cycle. 40 Ar- 39 Ar cooling ages indicate that much of the HRMC was exhumed at that time. Localisation of ASO tectonism in the eastern Arunta Province appears to be a result of thermal weakening associated with the ~480- 460 Ma Larapinta Event, which partitioned plate boundary stresses intocentral Australia.