Metamorphism in the New England Orogen, eastern Australia: a review

• Published in: Australian journal of earth sciences 2020-05, Vol.67 (4), p.453-478
• Main Authors: Jessop, K., Daczko, N. R., Piazolo, S.
• Format: Article
• Language: English
• Subjects: amphibolite; Amphibolites; blueschist; Cambrian; Compression; Contact pressure; Eclogite; eclogite facies; Exposure; Geological time; greenschist; High temperature; high-pressure-low-temperature (HPLT); high-temperature-low-pressure (HTLP); Identification; local metamorphism; Low pressure; Low temperature; Magma; Metamorphic facies; Metamorphism; Metamorphism (geology); New England Orogen; Ordovician; Orogeny; Phases; regional metamorphism; Rock; Rocks; Sedimentary facies; Serpentinite; Subduction; Subduction (geology); Tectonics
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1080/08120099.2020.1685000

This paper summarises current knowledge on metamorphism within the entire New England Orogen (NEO) of eastern Australia. Rocks recording metamorphic assemblages characteristic of each of the three metamorphic facies series (high, medium and low P/T) have been identified within the orogen. These include high P/T blueschists and eclogites, mid P/T orogenic metamorphism and low P/T contact aureoles and sub-regional high-temperature-low-pressure (HTLP) metamorphism (regional aureoles). Metamorphism is described as it relates to six tectonic phases of development of the NEO that together comprise two major cycles of compression-extension. Medium-high-grade contact metamorphism spans all six tectonic phases while low-grade burial and/or orogenic metamorphism has been identified for four of the six phases. In contrast, exposure of high P/T eclogites and blueschists, and generation of sub-regional low P/T metamorphism is restricted to extensional phases of the orogen. Hallmarks of the orogen are two newly identified zones of HTLP metamorphism, the older of which extends for almost the entire length of the orogen. KEY POINTS The orogen is dominated by low-temperature rocks while high-temperature amphibolite to granulite facies rocks are restricted to small exposures in HTLP complexes and contact aureoles. Blueschist metamorphism falls into two categories; that associated with subduction during the Currabubula-Connors continental arc phase occurring at depths of ∼13-30 km; and the other of Cambrian-Ordovician age, exposed within a serpentinite melange and associated with blocks of eclogite. The eclogite, initially from depths of ∼75-90 km, appears to have been entrained in the deep crust for an extended period of geological time. A comprehensive review of contact metamorphism in the orogen is lacking and as studies on low-grade metamorphism are more extensive in the southern part of the orogen than the north, this highlights a second research gap.