Middle Carboniferous-Early Triassic eclogite-blueschist blocks within a serpentinite mélange at Port Macquarie, eastern Australia: Implications for the evolution of Gondwana's eastern margin

Nutman, Allen P., Buckman, Solomon, Hidaka, Hiroshi, Kamiichi, Tomoyuki, Belousova, Elena and Aitchison, Jonathan (2013) Middle Carboniferous-Early Triassic eclogite-blueschist blocks within a serpentinite mélange at Port Macquarie, eastern Australia: Implications for the evolution of Gondwana's eastern margin. Gondwana Research, 24 3-4: 1038-1050. doi:10.1016/j.gr.2013.01.009


Author Nutman, Allen P.
Buckman, Solomon
Hidaka, Hiroshi
Kamiichi, Tomoyuki
Belousova, Elena
Aitchison, Jonathan
Title Middle Carboniferous-Early Triassic eclogite-blueschist blocks within a serpentinite mélange at Port Macquarie, eastern Australia: Implications for the evolution of Gondwana's eastern margin
Journal name Gondwana Research   Check publisher's open access policy
ISSN 1342-937X
Publication date 2013-01-01
Year available 2013
Sub-type Article (original research)
DOI 10.1016/j.gr.2013.01.009
Open Access Status Not Open Access
Volume 24
Issue 3-4
Start page 1038
End page 1050
Total pages 13
Place of publication Amsterdam, The Netherlands
Publisher Elsevier
Language eng
Abstract The New England Orogen of easternmost Australia is dominated by suites of Palaeozoic to earliest Mesozoic rocks that formed in supra-subduction zone settings at Gondwana's eastern margin. On the northern New South Wales coast at Rocky Beach, Port Macquarie, a serpentinite mélange carries rare tectonic blocks of low-grade, high-pressure, metamorphic rocks derived from sedimentary and igneous protoliths. Dominant assemblages are glaucophane. +. phengite. ±. garnet. ±. lawsonite. ±. calcite. ±. albite blueschists and lawsonite-bearing retrogressed garnet. +. omphacite eclogites. In some blocks with sedimentary protoliths, eclogite forms folded layers within the blueschists, which is interpreted as Mn/(Mn. +. Fe) compositional control on the development of blueschist versus eclogite assemblages. Review of previous studies indicates pressure-temperature conditions of 0.7-0.5. GPa and ≤. 450. °C. Three samples of high-pressure metasedimentary rocks contain Archaean to 251. ±. 6. Ma (Permo-Triassic) zircons, with the majority of the grains being Middle Devonian to Middle Carboniferous in age (380-340. Ma). Regardless of age, all grains show pitting and variable rounding of their exteriors. This morphology is attributed to abrasion in sedimentary systems, suggesting that they are all detrital grains. New in situ metamorphic zircon growth did not develop because of the low temperature (≤. 450. °C) of metamorphism. The Permo-Triassic, Devonian and Carboniferous zircons show strong heavy rare earth element enrichment and negative europium anomalies, indicating that they grew in low pressure igneous systems, not in a garnet-rich plagioclase-absent high pressure metamorphic environment. Therefore the youngest of these detrital zircons provides the maximum age of the metamorphism. A titanite. +. rutile porphyroblast within an eclogite has a U-Pb age of 332. ±. 140. Ma (poor precision due to very low U abundances of mostly <. 1. p.p.m.) and provides an imprecise direct age for metamorphism. In the south of the Port Macquarie area, the Lorne Basin ≥. 220. Ma Triassic sedimentary and volcanic rocks unconformably overlie serpentinite mélange, and provide the minimum age of the high-pressure metamorphism. Our preferred interpretation is that the 251. Ma zircons are detrital and thus the Port Macquarie high-pressure metamorphism is constrained to the end of the Permian-Early Triassic. Emplacement of the serpentinite mélange carrying the Rocky Beach high-pressure rocks might have been due to docking of a Permian oceanic island arc (represented by the Gympie terrane in southern Queensland?) and an Andean-style arc at the eastern Australian margin (expressed in the New England Orogen by 260-230. Ma north-south orientated magmatic belts). Alternatively, if the 251. Ma grains are regarded as having grown in thin pegmatites, then the dominant Devonian-Carboniferous detrital population still indicates a maximum age for the high pressure metamorphism of ca. 340. Ma. A ≤. 340. Ma age of metamorphism would still be much younger than the previously suggested ca. 470. Ma (Ordovician) age, which was based on Ar-Ar dating of phengites.
Keyword Blueschist-eclogite
Gondwana
New England Orogen
Port Macquarie
Serpentinites
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Geography, Planning and Environmental Management Publications
 
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Created: Fri, 27 Feb 2015, 20:31:03 EST by Helen Smith on behalf of School of Geography, Planning & Env Management