Timing relationships between pegmatite emplacement, metamorphism and deformation during the intra‐plate Alice Springs Orogeny, central Australia

Abstract

In the Harts Range (central Australia), the upper amphibolite facies to lower granulite facies, c. 480-460 Ma Harts Range Metamorphic Complex (HRMC), and the upper amphibolite facies, c. 340-320 Ma Entia Gneiss Complex are cut by numerous, generally peraluminous pegmatites and their deformed equivalents. The pegmatites have previously been interpreted as locally derived partial melts. However, SHRIMP U-Pb monazite and zircon dating of 29 pegmatites or their deformed equivalents, predominantly from the HRMC, reveal that they were emplaced episodically throughout almost the entire duration of the polyphase, c. 450-300 Ma intra-plate Alice Springs Orogeny. Episodes of pegmatite intrusion correlate with the age of major Alice Springs-age structures and with deposition of syn-orogenic sedimentary rocks in the adjacent Centralian Superbasin. Similar Alice Springs ages have not been obtained from anatectic country rocks in the HRMC, suggesting that the pegmatites were not locally derived. Instead, they are interpreted as highly fractionated granites, and imply that much larger parental Alice Springs-age granites exist at depth. The mechanism to allow repeated felsic magmatism in an intraplate setting, where all exposed rock types had a previous high-temperature history, is enigmatic. However, we suggest that episodic underthrusting and dehydration of unmetamorphosed Centralian Superbasin sedimentary rocks allowed crustal fertility to maintained over a c. 140 Ma interval during the intra-plate Alice Springs Orogeny.

Zircons from the Acraman impact melt rock (South Australia): Shock metamorphism, U–Pb and 40 Ar/ 39 Ar systematics, and implications for the isotopic dating of impact events

“…The latter somewhat ambiguous dataset suggests that there might have been one ($450 Ma) or two ($450 and $500 Ma) post-impact alteration events. It remains speculative whether these alteration ages are related to any of the Early Paleozoic orogenic events in Australia (e.g., the $514-490 Ma Delamerian Orogeny in southern Australia; Sandiford et al, 1998;Wingate et al, 1998;Foden et al 2006; the formation of the $450-380 Ma Lachlan Fold Belt in southeastern Australia; Foster and Gray, 2000; or the $450-300 Ma Alice Springs Orogeny in central Australia; Buick et al, 2008).…”

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

“…The BX1 event can be correlated to the Redbank Shear Event, while BX2-BX4 are related to the Alice Springs Orogeny. Specifically, the BX2 and BX3 events may correspond to the compressional 370-to 390-Ma Pertnjara-Brewers Movement recognised across the region (Buick et al 2008;McLaren et al 2009), while the 350-Ma BX4 breccia may have formed during exhumation at the waning stages of the Alice Springs Orogeny. Understanding the regional geological context of the genesis of ore bodies is essential for further mineral exploration targeting.…”

Zircon as the best mineral for P–T–time history of UHP metamorphism: A review on mineral inclusions and U–Pb SHRIMP ages of zircons from the Dabie–Sulu UHP rocks

“…The extremely stable nature of zircon and its high closure temperature for U-Pb diffusion means that its isotopic system is little disturbed by metamorphism and migmatitization. In situ U-Pb dating of zoned zircon can thus yield significant age information on the complex evolution history of its migmatitic host (Foster et al, 2001;Keay et al, 2001;Wallis et al, 2005;Wu et al, 2007;Buick et al, 2008;Ragozin et al, 2009). The Hf isotopic compositions of zircon in complex migmatites can be used not only to trace source characteristics, but also to reveal processes involved in generation of crustal melts and the crystallization of zircon during partial melting (Flowerdew et al, 2006;Wu et al, 2007;Liu et al, 2008).…”